The present invention concerns a process for producing polyhydroxy ethers and the unsymmetrical polyhydroxy ethers obtainable with the process. The process is based on the reaction of a multifunctional alcohol with an .alpha.,.beta.-unsaturated aldehyde or ketone and formaldehyde in the presence of an alkali hydroxide or alkaline earth hydroxide under conditions for the aldol/Cannizzaro reaction.
Polyhydroxy ethers of the di-, tri-, and polypentaerythritol type having the general formula: EQU (HOCH.sub.2).sub.3 --C--O--[CH.sub.2 OH).sub.2 CH.sub.2 --O].sub.n H
and corresponding polyhydroxy ethers based on trimethylolethane (TME) and trimethylolpropane (TMP) are becoming increasingly important as raw materials for special resins, lubricants, PVC stabilizers and PVC plasticizers. As polyhydroxy ethers of the above type have previously appeared only as small proportions of byproducts from the production of pentaerythritol, TME or TMP from acetaldehyde, propionaldehyde, or butyraldehyde, respectively, and formaldehyde form the combined aldol/Cannizzaro reaction, there has been no shortage of attempts to produce such polyhydroxy ethers as a goal (see, for instance, U.S. Pat. Nos. 2,325,589 and 2,490,567).
The yield of dipentaerythritol as a byproduct in the production of pentaerythritol can be increased somewhat, according to Japanese Patent Application 8 176 048 by using acrolein in place of part of the acetaldehyde. In this process, acetaldehyde and, if desired, part of the acrolein are put into an aqueous medium, and formaldehyde and acrolein are added dropwise, with the reaction being carried out at 0.degree. to 50.degree. C. in the presence of an alkali hydroxide. The yield of dipenta, based on acetaldehyde, was reported as 21 to 26%. According to the comparison example described in this process--reaction of pentaerythritol with acrolein and formaldehyde at 70.degree. C.--dipentaerythritol was obtained in a yield of 8.5%, along with polymers of acrolein.
Czechoslovak Patent 197 741 describes a process for producing dipentaerythritol by reaction of pentaerythritol with acrolein and formaldehyde at 0.degree. to 50.degree. C., at a molar ratio of pentaerythritol to acrolein of 0.2 to 3 and a molar ratio of formaldehyde to acrolein of 1 to 10. The entire amount of formaldehyde is placed in the reaction vessel, and acrolein is added. Pentaerythritol is added at the beginning of or during the reaction. In the recovery steps of the process, only a very small yield of dipentaerythritol was obtained instead of the high yield stated in the patent; see Comparison Example 1 herein below.
Soviet Union Patent 387 959 teaches a process similar to that of the Czechoslovak patent. In this patent, 0.1 to 2 moles of pentaerythritol are used per mole of acrolein and the reaction is done with formaldehyde at 50.degree. to 90.degree. C. The molar ratio of acrolein to formaldehyde to alkali hydroxide is 1:3 to 7:0.25 to 2. Pentaerythritol and water are placed in the reaction vessel, and acrolein and formaldehyde are added dropwise. In the recovery step of this process, too, the yields found for dipentaerythritol and tripentaerythritol, and the total yield, were substantially lower than as stated in the patent; see Comparison Example 2 herein below.
It is, then, an object of this invention to obtain dipentaerythritol in higher yields, using the process principle presented for dipentaerythritol, for example.
According to another object, the invention should also make it possible to produce the nonsymmetric polyhydroxy ethers, which were not known previously.